Field of the Invention
The present invention relates to an image pickup apparatus, a control method therefor, and a storage medium.
Description of the Related Art
Some image pickup apparatuses such as video cameras for professional use have a function of automatically adjusting black balance so as to fix defective pixels that appear later due to black level adjustments, cosmic radiation, or the like in a usage environment. By adjusting black balance, deviations of black level which occur with changes in the temperature of an image pickup device (image sensor), and defective pixels which appear later are corrected for. However, for an interchangeable-lens camera lens system, there are many interchangeable lenses which have a diaphragm which cannot fully shield light because of its mechanical structure. In a camera system equipped with such an interchangeable lens, the interchangeable lens is removed temporarily to mount a body cap on a camera main body so as to fully shield light, and black balance is automatically adjusted.
A technique to judge whether or not it is possible to properly perform automatic adjustment of black balance is described in, for example, Japanese Laid-Open Patent Publication (Kokai) No. 2013-98590). According to the technique described in Japanese Laid-Open Patent Publication (Kokai) No. 2013-98590, black balance is automatically adjusted on the condition that a luminance obtained in a state where the rate of darkening by a darkening action of a darkening member, which reduces the amount of light incident on an image pickup device, is controlled so as not to be the highest is equal to or smaller than a predetermined luminance value.
However, according to the technique described in Japanese Laid-Open Patent Publication (Kokai) No. 2013-98590, black balance is automatically adjusted on the precondition that light is fully shielded, and hence a problem arises because an adjustment error occurs when light cannot be fully shielded. For example, an indoor camera with a head, which is used, for example, for surveillance or at a bridal, is often placed at a high place, and it is thus uneasy for a user to mount a body cap on the camera. Thus, light cannot be fully shielded sometimes, making it impossible to automatically adjust black balance. Also, many indoor cameras with a head have no camera case, and hence an approach of providing a camera case with a light-shielding means cannot be taken, and moreover, due to flange back constraints, a camera main body often has no space where a member for use in fully shielding light is provided.